1. Field of the Invention
The present invention relates, in general, to communication systems that include cognitive radios and/or software defined radios (SDRs) to achieve efficient and reliable spectrum use without harmful interference to incumbent services such as television (TV) receivers, and, more particularly, to a method, and systems/devices configured to perform such a method, for controlling spectrum use by base stations and consumer premise equipment so as to allow unlicensed radios or other communication devices to operate in broadcast bands previously set aside for licensed users or services such as the TV broadcast bands. The method and related systems may be developed in some embodiments to comply with standards and protocols distributed by the IEEE 802.22 Working Group.
2. Relevant Background
It is a prominent goal of many countries to provide wireless broadband access or digital cellular communications to all or large portions of their citizens. In many countries, up to fifty percent or more of the population is in rural and remote areas away from cities and urban areas which can receive wireless services with existing infrastructure. Recent studies have indicated in the radio spectrum that licensed bands, such as TV or UHF bands, are underutilized. In the United States, the Federal Communications Commission (FCC) issued the “TV band Notice of Proposed Rule Making (NPRM)” that proposed allowance of unlicensed radios to operate in the TV broadcast bands as long as no harmful interference is caused to incumbent services such as TV receivers. In response, the Institute of Electrical and Electronics (IEEE) formed the IEEE 802.22 working group in 2004 to develop protocols for an interoperable air interface for use in spectrum allocated to TV broadcast service and enable providing wireless services such as broadband access with a point to multipoint wireless regional area network (WRAN). The WRAN system is intended to provide packet-based transport capabilities such as wireless broadband services such as Internet access, data transport, streaming video, VoIP, and other services that are presently available to much of the population using digital subscriber (DSL) technologies or digital cable modems.
WRAN technology has been initially targeted at wireless broadband or remote access for geographically dispersed, sparsely populated areas. The use of TV broadcast bands or UHF bands as a license exempt spectrum for WRAN provides a non-line of sight transmission range of up to 100 kilometers but more typically 30 to 70 kilometers, which is significantly greater than ranges available with WiFi and wireless networks. The target markets or users of the WRAN-based services are single family residential units, multi-dwelling units, small office/home office (SOHO) locations, small businesses, and remote public and private campuses. A WRAN system based on IEEE 802.22 protocols will likely make use, in a non-interfering manner, of unused TV broadcast channels, i.e., TV channels with bandwidths of 6, 7, and 8 MHz in a frequency range of 41 to 910 MHz (e.g., 54 to 862 MHz in the United States with a 6 MHz channel bandwidth).
An IEEE 802.22 system is generally a fixed point-to-multipoint wireless air interface in which the point is a base station (BS) that manages its own cell or coverage area and all associated consumer premise equipments (CPEs) or multipoints. Each CPE represents the user of the wireless services provided by the BS operator. During operations, the BS controls the medium access in its cell such as by setting the channel used for BS and CPE broadcasts to form the wireless link. The BS transmits in the downstream to the various CPEs, which respond back to the BS in the upstream direction, and these communications may be thought of as downlink and uplink communications or signals. The BS and CPE need to be designed to communicate without interfering with licensed or primary users. With this in mind, the BS manages spectrum or channel usage and uses sensing of existing channels to protect incumbent or primary users. To achieve distributed sensing, cognitive radio and/or software defined radio technology provides real-time sensing of spectrum usage. For example, the BS of the WRAN generally will be capable of performing distributed sensing which involves the CPEs sensing the spectrum and sending periodic reports to the BS. The sensing may be in-band to sense on the channel being used by the BS and CPE and/or out-of-band to sensing on the other channels (such as with an omni-directional antenna). Incumbent sensing also generally includes the BS periodically quieting the channel to allow in-band measurements to be carried out. If an incumbent or other use is detected by the BS based on reported measurements and preset interference detection thresholds, the BS makes the decision of whether to continue using the channel or to vacate the channel (i.e., to switch or hop to another vacant frequency). In addition to protecting incumbent or licensed services, WRANs under IEEE 802.22 are unlicensed and a BS servers a large area. As a result, coexistence amongst overlapping or coallocated cells must be managed and controlled by the BSs of the WRAN so that self-interference among neighboring BSs does not render the system useless.
In some proposed WRAN, each BS operates on a single channel for an operation period (e.g., up to 2 seconds as presently indicated by IEEE 802.22 protocols) and then performs sensing during a quite period (e.g., 20 to 100 milliseconds depending on sensing technology and mechanisms utilized by the BS and CPEs). If an incumbent or other use of the channel is sensed, the BS halts operations until the channel later becomes available. A single channel WRAN is effective in protecting incumbent services, but halting operations or data transmissions during a quiet time results in underutilization of the channel to transmit digital data (e.g., in about every 2 second period there is up to 100 milliseconds without transmissions).
To more effectively utilize the available channels, WRAN have been proposed in which each BS operates on two available channels. In these WRAN, frequency hopping is used such that when an operation period ends on one channel the BS and corresponding CPEs switch transmission to the other channel. The IEEE 802.22 protocol requires sensing prior to use of the second channels, and the BS is designed to perform distributed sensing of the second channel in parallel with the end of the operation period or transmission on the first channel. Hence, the BS can hop to the second channel at the end of the operation period, and there is no or little lag between consecutive operation periods, which results in significantly improved utilization of the available channels and enhanced quality of service (QoS). A problem, however, may arise if there are neighboring BSs with overlapping coverage or service areas. In these cases, collisions can occur when two or more neighboring BSs switch or hop to the same channel or to interfering channels at the same time or at substantially the same time. The channel that was selected for hopping by the two neighboring BSs appeared to be available to both BSs prior to the frequency hop or switch. Establishing and maintaining communications between one-hop neighboring BSs may be used to avoid collisions, but this may add complexity and design issues related to channel switching negotiations and in managing inter-system communications.
Hence, there remains a need for improved methods, and devices that implement such methods, for managing use and allocation of the radio spectrum in WRAN and other networks that communicate over channels in unused but licensed bands such as by using the TV bands of the radio spectrum. Preferably such methods and devices would be configured to be compliant with IEEE 802.22 protocols including protocols requiring protection of incumbent services such as digital and analog TV while providing higher utilization of available channels and controlling the risk of frequency hop collisions for neighboring BSs with no or limited inter-system communications and/or negotiations.